// 具体装饰器：添加牛奶
public class MilkDecorator extends CoffeeDecorator {
    public MilkDecorator(Coffee coffee) { super(coffee); }
    @Override
    public String getDescription() { return super.getDescription() + ", Milk"; }
    @Override
    public double getCost() { return super.getCost() + 0.5; }
}
